In the packaging industry, combining the forming, filling and capping function has become an industry standard, very often called “combi” or “block” machines, bringing equipment and installation compactness, bottle lightweight, ease of operation and industrial simplification. Hydraulic forming of the container brings the opportunity of an even more compact machine for the same result, as the forming and the filling are done in one step, and removes the need of using expensive and energy inefficient production of compressed gas, such as air.
Hydraulic forming allows rather high forming pressures as high as 50 bars, thus creating a very good impression of the formed container.
In hydraulic forming process, the preform is typically made of a thermoplastic material which can be chosen for instance among the following: thermoplastic polyesters such as PET, PEN, PEI, PTT, PLA, PEF, polyolefins such as PP, HDPE, LDPE, styrene based materials such as PS, ABS, others such as PVC.
Another significant advantage of hydraulic forming, whether assisted by stretching or not, resides in the fact that containers can be filled and formed at very high speed. Typically, the forming time (not including equilibration or cooling time) will range from 0.1 seconds to 1.0 second and more specifically from 0.1 to 0.2 second, whereas traditional filling for either ambient temperature filling of still products such as for water, carbonated drinks filling, hot filling of still products, or aseptic filling of sensitive products, requires from 4 to 15 seconds of filling time.
This huge advantage carries a difficulty which is about evacuating or removing the air contained in the preform. If not removed, and because of the high liquid pressure used, this air will dissolve in the filled product and may generate some issues:
for still water: change of dissolved gas composition, change of acidity, foaming;
for carbonated water or any carbonated drinks: change in carbonation rate as the partial pressure of nitrogen and oxygen will increase, forcing CO2 partial pressure to decrease (the total pressure which is the sum of the partial pressures do not change). Also, foaming will occur. Shelf life and quality of the product will be affected; and
for hot filled products and aseptically filled sensitive products: increase of dissolved oxygen, meaning lower shelf life for oxygen sensitive products and the risk of foaming will be increased as well.
In the conventional air forming methods, the volume of air to remove is close to the volume of the bottle. During the filling process, the air is evacuated by a venting device during the duration of the filling operation.
In hydraulic forming, especially with high speed forming, the time to vent or evacuate the preform is very short, so that the air evacuation is difficult to control, with a high risk of losing product during this operation.
WO-A-2010/003873 discloses a method and an apparatus of the above-mentioned type, for injecting beverage into a preform and promoting the expansion of the preform. An injection head closes the preform. Sterilizing steam can be injected through a first conduit of the injection head. The only other conduit of the injecting head injects beverage, so air cannot be expelled from the preform.
US-2011/0300249 discloses the injection of steam in a preform as a sterilizing alternative to a sterilization obtained by a hot-fill process or obtained with a sterilization liquid such as liquid peroxide. The sterilizing process is described as the first step of a hydraulic forming process of a container.